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  #1  
Old 09-09-2002, 04:39 PM
Bob Boyer
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W126 A/C vacuum line supply etc.

Have '88 420 SEL.

This weekend, got my blower fan back in high-speed order (required only bending one of the contact points back).

blows almost cold. BUT:

I am getting only some air from center vent. Here's what happens:

When the dash position in A/C is on, get some air from center vent, but still most from defrost section. When bi-level switch pushed, reverts to only top and bottom and absolutely no center vent. So----I surmise the damper is working to some degree.

I believe that I either have a slightly stuck diaphram door controlling center vent, or a loose vacuum line. The main vacuum line evident in engine compartment seems fine. So I guess I need some guidance here.

Any quick tips, without removing the dash (last resort)? Can I check vacuum line beyond the firewall or inside compartment at a typically weak point? Is there such a point?

Can I gerrymander or try to unstick a possible weak diaphram door reglating to center vent?

Can I get/download a diagram of the A/C vacuum lines for a 126?

Any educated assistance I can get on the above would be so much appreciated!!

Thanks.
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  #2  
Old 09-10-2002, 12:41 AM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
I'd get a MitiVac hand vac pump at the local autoparts store -- price varies from $35-45, and worth every penny.

Connect to the green plastic line in the engine compartment and see if it holds vac. If so, check for vac leaks up front (the check valve, at little blue and black plastic thing in the line -- may only be black) can crack and leak off the vac.

If not, you have either a leak or a bad pushbutton control unit. You can pull the PBC from the dash and check each servo by attaching the hand pump and seeing if they hold and operate. Much more work to replace bad ones, but at least you would know what works and doesn't.

It sounds to me like you have low vac or a bad AC servo. The system defaults to defrost if the vac fails or servo dies -- my 300 D had some bad vac actuators for the EGR and air recirc on the turbo, and the resultant vac leak caused my AC to blow mostly up the windsheild. Fixing the actuators repaired the AC.

Check all the vac lines in the engine compartment -- they are old enough now to have the rubber going bad. They either get rock hard (and leak) or soft and mushy, shedding black powder (and leak). There is also a vac reservior for the climate control, and the rubber bushing there can leak, too.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
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  #3  
Old 09-10-2002, 08:29 AM
Bob Boyer
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Thanks much, Peter. Will check the vacuum lines. That's where I believe my problem is.
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  #4  
Old 09-10-2002, 08:42 AM
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Join Date: Mar 2000
Location: Gainesville FL
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Unless someone has been monkeying with the lines they are NOT the problem. The problem will be either the center duct vacuum element, one of the defrost elements, or the recirc door element.

They all have vacuum on them in the AC position. A leak in any one reduces the available vacuum to the rest. The easiest test is to go behind the glovebox and with a vacuum diagram decide which lines go to these elements from the switchover valve block. Pull the lines one at a time and pull a vacuum (one can do it with one's own lungs easy enough, suck and put your tungue on it; if it leaks there will never be anything for the tongue to hold)
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Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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  #5  
Old 09-10-2002, 08:45 AM
Bob Boyer
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Thanks, Steve. simple question: (may not want to know the answer, though):

How can I get behind the glovebox? Can you explain?

thanks again.
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  #6  
Old 09-10-2002, 08:46 AM
Bob Boyer
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****ALSO:

Can I get the vacuum line diagram?
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  #7  
Old 09-10-2002, 09:31 AM
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Join Date: Mar 2000
Location: Gainesville FL
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The vacuum diagram is in the CD-Rom for chassis 126. If you are serious about working on such projects, this level of info is imperative.

It would also show you how to remove the glovebox and lower dash panel. Basically the panel is held with 4 screws and the glove box comes straight out after pulling all the clips out. Remove the light and disconnect the wires.
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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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  #8  
Old 09-10-2002, 09:36 AM
Bob Boyer
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Thanks, Steve.

Guess I should bite the bullet and buy the CD.

By the way:

my daughter is a sophomore at UF. Was just up in Gainesville, and have been there 4 times over the last 1.5 yrs. Seems to be every 6 months or so. The cafes downtown are great.

I live in Pembroke Pines and have office in Aventura, so the ride to gainesville is about 5.5 hrs with stops. It's a good ride for the car, though, as it kind of exercises everything.

Thanks again.

Bob
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  #9  
Old 09-10-2002, 10:40 AM
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You must be a slow driver, I have a sister in Coral Gables and it takes me less than 5 hours to get there.

Our shop is about a half mile from those downtown shops and my house is another three quarters mile behind the small lake on South Main Street.
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Steve Brotherton
Continental Imports
Gainesville FL
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33 years MB technician
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  #10  
Old 09-10-2002, 10:45 AM
Bob Boyer
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Steve:

Remember, I said 2 stops. Also, if you had seen the number of smolies out there 2 weeks ago, you wouldn't have made it in under 5.

Bob
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  #11  
Old 09-10-2002, 10:46 AM
Bob Boyer
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And by the way, next time, I'll make an appt. with you while I'm up there.
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